The present invention relates to an image heating device suitable when used as a fixing device (for fixing a toner image on a recording material under application of heat and pressure) mounted in an image forming apparatus, such as a copying machine, a printer, a facsimile, or a multi function machine having a plurality of functions of these machines.
As the fixing device (image heating device) used in the image forming apparatus of an electrophotographic type, a fixing device of a film type including a fixing film moving in contact with a heating member (heater) (hereafter, the fixing film is referred to as a rotatable member) has been known (Japanese Laid Open Patent Application 2006 293225). This fixing device has good heat transfer efficiency and, therefore, has an advantage such that a time from a start of energization to the heating member (heater) until a temperature reaches a fixable temperature is short and a time, until an image formed on a first sheet is outputted, is short. Further, the fixing device also has an advantage such that electrical power consumption during a stand by state waiting for a print instruction is low, and thus, is introduced in many image forming apparatuses in recent years.
In such a fixing device of the film type, at a position opposing an end edge of the rotatable member, a flange (rotatable member supporting member) for regulating a position of the rotatable member with respect to a thrust direction is provided. The flange is engaged with an electroconductive (device) frame (casing of the fixing device) formed with a metal plate.
By applying an electrical bias voltage to the rotatable member, unfixed toner on a recording material is prevented from being deposited on a rotatable member and a pressing roller for forming a nip in cooperation with the rotatable member.
Further, a constitution in which, in order to prevent leakage of the bias voltage applied to the rotatable member to the frame, a distance between the rotatable member and the frame satisfies an electrical insulation distance is employed. That is, the fixing device is constituted so as to sufficiently ensure a size of a rotatable member end portion regulating surface with respect to a radial direction of the flange and so as to ensure electrical air clearance and creepage distance between the rotatable member end edge and the frame.
However, with recent downsizing of the image forming apparatus, when a configuration space of internal component parts of the fixing device decreases, the flange is required to decrease the rotatable member end portion regulating surface, so that it has become difficult to ensure the electrical air clearance and creepage distance.
Thus, the fixing device that compatibly realizes the downsizing of the fixing device (image heating device) and ensuring of the electrical insulation distance between the rotatable member and the frame is desired.